1. Field of the Invention
The present invention relates to purification of an exhaust gas of a diesel engine vehicle. More particularly, the present invention relates to a purification system for variable post injection in LP EGR and the control method for the same.
2. Description of Related Art
Nitrogen oxides (NOx) and particulate matters (PM) are principal air pollution material of a diesel engine vehicle. Therefore, they are under strict emission regulation of a diesel engine.
Several technologies have been developed to cope with the emission regulation of the diesel engine. For example, fuel injection timing may be delayed. In addition, exhaust gas recirculation (EGR) has been enhanced such that NOx exhaust may be reduced. In addition, combustion characteristic of the diesel engine has been improved so as to reduce PM.
Such technologies for complying with the diesel engine emission regulation may be classified into an engine improving technology and a post-processing technology. Examples of the post-processing technology for reducing the principal exhaust gas of the diesel engine are (1) oxidation catalyst for purifying high boiling point hydrocarbon (HC) among the particulate matters, (2) a DeNOx catalyst for decomposition or reduction of the NOx under an excess oxygen atmosphere, and (3) a diesel particulate filter (DPF) system filtering the PM.
Among such a post-processing technology, a simultaneous NOx-PM reduction apparatus having a lean NOx trap (LNT) and a Diesel particulate filter (DPF) is also included. Regarding the simultaneous NOx-PM reduction apparatus, it is believed that simultaneous generation of the LNT and DPF is not possible. In addition, the regeneration of LNT is required to be performed in a rich range of an air/fuel ratio, and thus the regeneration of the LNT causes a substantial amount of PM.
The DPF system has a merit that PM is sufficiently trapped so as to substantially decrease an exhaust of the PM. However, apparatus and/or algorithm for a regeneration control of the trapped PM by an after-burning thereof have not sufficiently investigated. Consequently, in the state of the art, durability of the DPF is still problematic since an excessive heat may be produced during the regeneration of the filter thereby causing a damage of the DPF. In addition, during a large scale of EGR for removal of the NOx, a substantial amount of the PM is produced.
Therefore, in this case, a PM trapping limit of a catalyst support of the DPF easily becomes saturated, and this may be a cause of the damage of the support of the DPF during an active regeneration of the DPF.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.